This invention relates to rotors for magnetomotive devices and, more particularly, to such rotors for small internal combustion engines having a magnet and metallic core molded within the body of a synthetic plasic material. The core is structurally independent of the plastic body and is constructed so that at high rotational speeds, centrifugal forces serve to generate clamping forces on the magnet by the core to compensate for the inertial effect of such high speeds.
In the past, rotors for magnetomotive devices which combined permanent magnets and pole pieces and usually served as the engine flywheel, were generally formed of a metallic material, such as aluminum or zinc or a composite thereof, of suitable strength to withstand the inertial stresses of high rotational speeds.
Prior art methods of mounting permanent magnets and pole shoes in magneto flywheel rotors included the casting of the magnet and the pole shoe group directly into the flywheel body which were of sufficient strength to hold the parts in assembled relation at high rpm. It has also been proposed to affix the magnet and pole shoe group to the rotor by fasteners, such as dowels, pins, screws or the use of special bonding agents.
U.S. Pat. No. 4,179,634 to Burson and U.S. Pat. No. 4,482,831 to Notaras disclose the use of dowel and pin type fasteners and specially shaped cavities for retaining the pole shoe magnet group within the die-cast aluminum rotor. When such rotors are operated at high speeds, they are subjected to great centrifugal force and the individual components, especially the high density permanent magnet, tend to separate from the rotor. As a result, synthetic plastic materials have not generally been used in such rotor structures.
Accordingly, the principal object of this invention is to provide an improved rotor for magnetomotive devices composed of an injection molded synthetic plastic body in which is disposed an integral flux carrying core member constructed with magnet retaining arms adapted to exert clamping forces on the magnet so that centrifugal forces generated by the rotation of the rotor prevent high speed failure of the rotor caused by inertial separation of the arms of the core member.
Another object of this invention is to provide an improved rotor of the above type which the core is integral and includes a hub portion mounted on the drive shaft of the engine, a counterweight and magnet clamping arm portions group disposed diametrically opposite the counterweight whereby the unit is structurally independent of the synthetic plastic body of the rotor.
A further object of this invention is to provide an improved rotor of the above type in which the core comprises a resiliently flexible laminated ferrous metal structure.